In circuits involving purely sinusoidal V and I of the same frequency,
the power waveform is actually a true sinusoidal function, except with a
D.C. offset. It doesn't at all resemble the output from a full wave
rectifier. The D.C. offset is the average value, and the frequency of
the sine portion is twice the frequency of V or I.

Roy Lewallen, W7EL

Jim Kelley wrote:

Richard Harrison wrote:

What is the value in watts or joules per second when seconds equal
zero? I venture an answer: It is the V x I x cos. theta at that instant,
but since work is power x time, it won`t do anything for you in zero
seconds.


I think you have a slight misconception about the meaning of
instantaneous power. AC power is a pseudo-sinusoidal function with
respect to time, like that of full-wave rectifier. The function has a
value, an instantaneous amplitude, at any time t which represents the
rate at which energy in Joules is moving past a point x at time t. It
may not be a terribly useful thing to know, but it isn't a ficticious
quantity.

73, ac6xg